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Edward Thomas Jr

Publications and source records attributed to Edward Thomas Jr.

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Electron magnetization effects on carbonaceous dusty nanoparticles grown in $Ar/C_2H_2$ capacitively coupled nonthermal plasma

Carbonaceous dusty nanoparticles spontaneously grow in nonthermal plasmas from a gas mixture of argon and acetylene. These particles levitate and grow within the bulk plasma for a duration known as the growth cycle ($T_c$), after which they gradually move away. In experiments operating at 500 milliTorr, the particles reach a maximum radius of approximately 250 nm for $T_c \sim$ 121 s. However, the introduction of weak magnetic fields reduces both the maximum radius and $T_c$. The modified electron Hall parameter ($H_e'$), which quantifies the degree of electron magnetization, increases linearly with the magnetic field strength, transitioning from unmagnetized electrons ($H_e' < 1$) to magnetized electrons ($H_e' > 1$). $T_c$ gradually decreases to around 40 s until $H_e' \sim 1$ at approximately 330 Gauss, after which it remains roughly constant for fields up to about 1020 Gauss. Additionally, with increasing magnetic field strength, the dust growth rate initially decreases to $H_e' \sim 1$, then increases slightly again. These results demonstrate that the onset of electron magnetization at can control the growth of nanoparticles from chemical precursors in nonthermal plasmas, which is relevant for industrial applications.

physics.plasm-ph

Comparing growth of titania and carbonaceous dusty nanoparticles in weakly magnetised capacitively coupled plasmas

This study compares the growth cycles and spatial distribution of dust cloud for titania and carbonaceous dusty nanoparticles in capacitively coupled radiofrequency plasmas, with and without the presence of a weak magnetic field of approximately 500 Gauss. Findings on cycle time, growth rate, and spatial distribution of dust cloud are discussed. The growth of nanoparticles in these plasmas is cyclic, with particles reaching their maximum size and subsequently moving out of the plasma, followed by the generation of a new particle growth cycle. The presence of the magnetic field speeds up the growth cycle in both plasma. The magnetic field also makes the spatial distribution of the two dust cloud different from each other. Langmuir probe measurement of the background plasma parameters such as electron temperature and floating potential reveal radial variations in floating potential but not electron temperature. Furthermore, the magnetic field changes the radial variation of floating potential. These measurements, however, are not sufficient to explain why the two dust clouds appear differently. It is possible that the differences occur due to a gradient in the radial distribution of the magnetic field.

physics.plasm-ph

Research Opportunities in Plasma Astrophysics

Major scientific questions and research opportunities are described on 10 unprioritized plasma astrophysics topics: (1) magnetic reconnection, (2) collisionless shocks and particle acceleration, (3) waves and turbulence, (4) magnetic dynamos, (5) interface and shear instabilities, (6) angular momentum transport, (7) dusty plasmas, (8) radiative hydrodynamics, (9) relativistic, pair-dominated and strongly magnetized plasmas, (10) jets and outflows. Note that this is a conference report from a Workshop on Opportunities in Plasma Astrophysics (WOPA, https://w3.pppl.gov/conferences/2010/WOPA/) in January 2010, that attracted broad representation from the community and was supported by the U.S. Department of Energy, National Aeronautics and Space Administration, National Science Foundation, American Physical Society's Topical Group for Plasma Astrophysics and Division of Plasma Physics, and Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas. Although there has been much planning and many developments in both science and infrastructure since the report was written, most of the motivation, priorities, problems and technical challenges discussed therein remain unaddressed and are relevant at the time of posting.

physics.plasm-ph